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Abstract:

A water-reducible mixture of (meth)acrylic copolymers having a hydroxyl
number of from 40 mg/g to 250 mg/g, an acid number of from 15 mg/g to 80
mg/g, a weight average molar mass Mw from 9 kg/mol to 40 kg/mol and
a glass transition temperature Tg from -40° C. to 80°
C., based on polymerised monomers comprising at least one alkyl ester A
of an olefinically un-saturated carboxylic acid having from 1 to 8 carbon
atoms in the alkyl group, at least one hydroxy functional alkyl ester B
of an olefinically unsaturated carboxylic acid, at least one aliphatic
compound C that has both hydroxy and carboxyl functionalities, or which
is a lactone or a cyclic lactone, at least one vinyl monomer D which does
not comprise a moiety derived from an olefinically unsaturated carboxylic
acid, at least one olefinically unsaturated carboxylic acid E, a process
for its preparation, and a method of use thereof in the preparation of
paints.

Claims:

1. A water-reducible mixture of (meth)acrylic copolymers having a hydroxyl
number of from 40 mg/g to 250 mg/g, an acid number of from 15 mg/g to 80
mg/g, a weight average molar mass Mw from 9 kg/mol to 40 kg/mol and
a glass transition temperature Tg from -40.degree. C. to 80.degree.
C., based on polymerised monomers comprising at least one alkyl ester A
of an olefinically unsaturated carboxylic acid having from 1 to 8 carbon
atoms in the alkyl group, at least one hydroxy functional alkyl ester B
of an olefinically unsaturated carboxylic acid, at least one aliphatic
compound C that has both hydroxy and carboxyl functionalities, or which
is a lactone or a cyclic lactone, at least one vinyl monomer D which does
not comprise a moiety derived from an olefinically unsaturated carboxylic
acid, at least one olefinically unsaturated carboxylic acid E.

3. The water-reducible mixture of (meth)acrylic copolymers of claim 1
which also comprises polymerised monomers selected from alkyl esters G of
an olefinically unsaturated carboxylic acid having from 9 to 40 carbon
atoms in the alkyl group.

4. The water-reducible mixture of (meth)acrylic copolymers of claim 1
which comprise moieties derived from the said monomers in mass fractions
of from 10% to 40% of monomers A, from 5% to 35% of monomers B, from 1%
to 25% of monomers C, from 20% to 50% of monomers D, and from 2% to 20%
of monomers E, where the sum of all mass fractions equals 100%.

5. The water-reducible mixture of (meth)acrylic copolymers of claim 2
which comprise moieties derived from the said monomers in mass fractions
of from 10% to 50% of monomers A, from 5% to 35% of monomers B, from 1%
to 25% of monomers C, from 20% to 50% of monomers D, from 2% to 20% of
monomers E, and from 0.1% to 3.0% of monomers F, where the sum of all
mass fractions equals 100%.

6. The water-reducible mixture of (meth)acrylic copolymers of claim 3
which comprise moieties derived from the said monomers in mass fractions
of from 10% to 50% of monomers A, from 5% to 35% of monomers B, from 1%
to 25% of monomers C, from 20% to 50% of monomers D, from 2% to 20% of
monomers A, and from 0.2% to 15% of monomers G, where the sum of all mass
fractions equals 100%.

7. A process of making the mixture of copolymers of claim 1 in a two-step
reaction, wherein, in the first step, a hydroxy functional acrylate
copolymer 1 is prepared by polymerising a mixture of monomers containing
at least one monomer each of the groups of A, B, C, and D to obtain a
hydroxy functional copolymer 1, in a separate second step, a carboxyl
functional copolymer 2 is prepared by polymerising a mixture of monomers
containing at least one monomer each of the groups of A, B, and E, and in
a third consecutive step, performing a condensation reaction between
copolymers 1 and 2 under esterification conditions to obtain, under
consumption of from 0.5% to 20% of the carboxyl groups of copolymer 2
which carboxyl groups are consumed by esterification with hydroxyl groups
of copolymer 1, a polymer 12, in a mixture with unreacted copolymers 1
and 2.

8. The process of claim 7 wherein in the preparation of the hydroxy
functional copolymer 1, at least one of the monomers of groups of F and G
are also present in the said mixture of monomers, wherein the monomers of
group F are epoxy functional alkyl esters of an olefinically unsaturated
carboxylic acid, and the monomers G are alkyl esters of an olefinically
unsaturated carboxylic acid having from 9 to 40 carbon atoms in the alkyl
group.

9. The process of claim 8 wherein the said mixture of copolymers of claim
1 is neutralised by adding a neutralisation agent selected from the group
consisting of aqueous alkali, ammonia, and organic amines.

10. A method of use of the said mixture of copolymers of claim 1 in the
preparation of paints comprising neutralising the said mixture by adding
a neutralisation agent selected from the group consisting of aqueous
alkali, ammonia, and organic amines, diluting with water, adding thereto
at least one additive selected from the group consisting of crosslinkers,
defoamers, wetting agents, levelling agents, coalescing agents,
dispersing agents, and antisettling agents, pigments and fillers, and
homogenising this mixture.

Description:

[0002]In automotive coatings, there is a need for coating compositions
leading to coating films having, at the same time, good mechanical,
chemical, and optical properties, such as hardness, elasticity, scratch
resistance, resistance against dilute acids and water, as well as high
gloss and low haze.

[0003]It has been known that scratch resistant coatings can be obtained
from hydroxy-functional solution (meth)acrylic copolymers which are
modified with lactones. In U.S. Pat. No. 4,546,046, for example, solvent
borne coating compositions for automotive coatings are described that are
based on ε-caprolactone-modified (meth)acrylic copolymers and
aminoplast cross-linking agents. The (meth)acrylic copolymers comprise
moieties based on reaction products of carboxy-functional or
hydroxy-functional unsaturated monomers and ε-caprolactone.
Modification of the said monomers with ε-caprolactone may be made
by adding the lactone to the said monomers before or during the
polymerisation, which said monomers react under ring opening and addition
to the lactone under formation of chain-extended vinyl monomers having
hydroxyl or carboxyl functionalities, or after the polymerisation
reaction, in the form of a polymer analogous reaction.

[0004]While such modification leads to improved scratch resistance of the
coating film formed from such binder, the optical properties of the
coating film are impaired by such modification.

[0005]It is therefore an object of the invention to provide a binder which
leads to coating films having both the improved scratch resistance of the
prior art, yet also improved gloss and reduced haze.

[0006]It is a further object of the present invention to provide a water
reducible binder having the said properties.

[0007]These objects of the present invention are achieved by
water-reducible hydroxy-functional binders based on (meth)acrylic
copolymers which, when used in one-component and two-component coating
compositions, produce flexible scratch resistant coatings with very good
chemical and acid resistance. When applied as a clear coat to
solvent-based base coats in particular, there is no or only a slight
dissolution of the base coat.

[0008]The present invention is directed to a water-reducible mixture of
(meth)acrylic copolymers having a hydroxyl number of from 40 mg/g to 250
mg/g, an acid number of from 15 mg/g to 80 mg/g, a weight average molar
mass (Mw) from 9 kg/mol to 40 kg/mol and a glass transition
temperature Tg from -40° C. to 80° C., based on
polymerised monomers comprising at least one alkyl ester A of an
olefinically unsaturated carboxylic acid having from 1 to 8 carbon atoms
in the alkyl group, at least one hydroxy functional alkyl ester B of an
olefinically unsaturated carboxylic acid, at least one aliphatic compound
C that has both hydroxy and carboxyl functionalities, or which is a
(cyclic) lactone, at least one vinyl monomer D which does not comprise a
moiety derived from an olefinically unsaturated carboxylic acid, at least
one olefinically unsaturated carboxylic acid E, and optionally, at least
one epoxy functional alkyl ester F of an olefinically unsaturated
carboxylic acid, and also optionally, at least one alkyl ester G of an
olefinically unsaturated carboxylic acid having from 9 to 40 carbon atoms
in the alkyl group.

[0009]The present invention is also directed to a process of making the
said mixture of copolymers in a two-step reaction, wherein, in the first
step, a hydroxy functional acrylate copolymer 1 is prepared by
polymerising a mixture of monomers containing at least one monomer each
of the groups of A, B, C, D, and optionally, at least one of the groups
of F and G, to obtain a hydroxy functional copolymer 1, in a separate
second step, a carboxyl functional copolymer 2 is prepared by
polymerising a mixture of monomers containing at least one monomer each
of the groups of A, D, and E, and in a third consecutive step, performing
a condensation reaction between polymers 1 and 2 under esterification
conditions to obtain, under consumption of from 0.5% to 20% of the
carboxyl groups of copolymer 2 which carboxyl groups are consumed by
esterification with hydroxyl groups of copolymer 1, a polymer 12, in a
mixture with unreacted copolymers 1 and 2.

[0010]Polymerisation for each of the polymers 1 and 2 is usually conducted
in a solvent that is inert under the conditions of a radically initiated
polymerisation, such as alcohols, esters or ketones. It is also possible
to use a cyclic lactone C, or a monomer according to A which has a low
tendency for copolymerisation, as solvents in the polymerisation step.
These compounds are incorporated into the polymer in the final phase of
the polymerisation process and thus help to reduce the amount of solvent
used which has to be distilled off afterwards.

[0011]The esterification process is usually conducted when the solvents
are fully or nearly fully removed, at a temperature of from 100°
C. to 160° C., and conducted for a sufficient amount of time to
consume from 0.5% to 20% of the carboxyl groups of polymer 2, and to
render the mixture of condensation product 12 and unreacted polymers 1
and 2 water-dilutable. This can be monitored by taking samples from the
reaction vessel and diluting it with water after at least partial
neutralisation of the remaining acid groups.

[0012]As monomers A, alkyl esters of alcohols A1 having from 1 to 8 carbon
atoms in the alkyl group, of olefinically unsaturated carboxylic acids A2
are preferred. Particularly preferred are esters of linear or branched
aliphatic olefinically unsaturated carboxylic acids A21 having from one
to three, preferably one or two, carboxylic acid groups per molecule.
Particularly preferred are esters of monocarboxylic olefinically
unsaturated carboxylic acids such as acrylic acid, methacrylic acid,
crotonic acid, isocrotonic acid, and vinyl acetic acid. It is also
possible to use dialkyl esters of dicarboxylic olefinically unsaturated
acids A22, such as maleic acid, fumaric acid, citraconic acid, itaconic
acid, and mesaconic acid. It is especially preferred to use branched or
linear C1- to C8-alkyl esters of acrylic and methacrylic acids,
alone, or in mixture. With particular preference, the esters of methanol,
ethanol, n- and iso-propanol, n-butanol, n-hexanol, n-octanol, and
2-ethyl hexanol, with acrylic and methacrylic acids are used.

[0013]As monomers B, esters of polyhydric, preferably dihydric, linear,
branched and cyclic aliphatic alcohols B1 with acids B2 which are
selected from the same group as mentioned under A2 are used, which esters
are hydroxy functional, i.e. on the average, the number of hydroxyl
groups per molecule of B1 is larger than the number of acid groups in the
acids B2. Preferably, the average number of remaining (i.e.
non-esterified) hydroxyl groups per molecule of monomer B is from 0.5 to
1.5, particularly preferably, from 0.7 to 1.3, and especially preferred,
from 0.8 to 1.2. Preferred are esters of dihydric alcohols such as
ethylene glycol, 1,2- and 1,3-propane diol, 1,4-butane diol, neopentyl
glycol, 1,6-hexane diol, and trimethyl 1,6-hexane diol with
monocarboxylic unsaturated carboxylic acids such as acrylic or
methacrylic acids. Esters with more than one hydroxy group per molecule
are preferably glycerol mon(meth)acrylate and pentaerythritol
di(meth)acrylate, while an average hydroxy functionality of less than one
is achieved by mixing esters A with monohydroxy esters according to B.

[0014]As monomers C, aliphatic linear, branched or cyclic hydroxy acids
may be used which preferably have from 2 to 20 carbon atoms, and at least
one hydroxyl and at least one carboxyl group. It is also possible to use
oligomeric compounds that are poly-oligoesters from such hydroxy acids,
such as oligo- or poly-caprolactone, oligo- or poly-butyrolactone, and
oligo- or poly-valerolactone, cyclic lactones such as the said lactones
themselves, and mixed oligo- and polyesters from lactones such as those
mentioned. Particularly preferred are gamma-butyrolactone,
delta-valerolactone, and epsilon-caprolactone.

[0015]As monomers D, which do not comprise a moiety derived from an
olefinically unsaturated carboxylic acid, all vinyl monomers can be used
that fulfill this requirement, such as esters of vinyl alcohol or allyl
alcohol with acids, such as vinyl acetate, vinyl propionate, or the allyl
and vinyl esters of branched aliphatic carboxylic acids where the
branching is in the alpha position relative to the carboxyl group, such
as isobutyric acid, 2-methylvaleric acid, pivalic acid, neohexanoic acid,
2-methyl oenanthic acid, 2-ethylhexanoic acid, neooctanoic acid, and
neodecanoic acids, or mixtures thereof, as well as vinyl or allyl ethers,
vinyl ketones, and vinyl aromatic monomers can preferably be used that
have at least one olefinic unsaturation and at least one aromatic moiety,
such as styrene, substituted styrenes such as chlorostyrene, methoxy
styrene, vinyl toluene, alpha-methyl styrene, divinyl benzene, and vinyl
naphthalene. Preferably, the amount-of-substance fraction of divinyl or
polyvinyl monomers having more than one olefinic unsaturation is kept
below 10% because gelation may occur if this amount is too high.

[0017]As monomers F, esters of epoxy functional alcohols F1 such as
glycidyl alcohol with olefinically unsaturated carboxylic acids B21 are
preferred, as well as ethers of epoxy functional alcohols such as
glycidyl alcohol with olefinically unsaturated alcohols F2 such as allyl
alcohol. Preferred compounds F are glycidyl methacrylate and glycidyl
acrylate, as well as diglycidyl maleinate.

[0019]It has been found in the investigations that have led to the present
invention that a ratio of the amount of substance of monomers C to the
amount of substance of monomer B should not exceed 1.9, preferably not
exceed 1.85, and particularly preferably, not exceed 1.8. Especially
favourable results have been achieved if the is ratio does not exceed
1.7.

[0020]In a preferred embodiment, the water-reducible mixture of
(meth)acrylic copolymers comprises moieties derived from the said
monomers A, B, C, D, and E in mass fractions of from 10% to 50% of
monomers A, from 5% to 35% of monomers B, from 1% to 25% of monomers C,
from 20% to 50% of monomers D, and from 2% to 20% of monomers E, where
the sum of all mass fractions equals 100%.

[0021]In a further preferred embodiment, the water-reducible mixture of
(meth)acrylic copolymers comprises moieties derived from the said
monomers A, B, C, D, E, and F in mass fractions of from 10% to 50% of
monomers A, from 5% to 35% of monomers B, from 1% to 25% of monomers C,
from 20% to 50% of monomers D, from 2% to 20% of monomers E, and from
0.1% to 3.0% of monomers F, where the sum of all mass fractions equals
100%.

[0022]In a further preferred embodiment, the water-reducible mixture of
(meth)acrylic copolymers comprises moieties derived from the said
monomers A, B, C, D, E and G in mass fractions of from 10% to 50% of
monomers A, from 5% to 35% of monomers B, from 1% to 25% of monomers C,
from 20% to 50% of monomers D, from 2% to 20% of monomers E, and from
0.2% to 15% of monomers G, where the sum of all mass fractions equals
100%.

[0023]In a particularly preferred embodiment, the water-reducible mixture
of (meth)acrylic copolymers comprises moieties derived from the said
monomers in mass fractions of from 15% to 40% of monomers A, from 10% to
30% of monomers B, from 2% to 20% of monomers C, from 25% to 45% of
monomers D, from 3% to 15% of monomers E, and optionally, from 0.2% to
2.0% of monomers F, and also optionally, from 2% to 12% of monomers G,
where the sum of all mass fractions equals 100%.

[0024]The hydroxy functional copolymer 1 preferably has a hydroxyl number
of from 50 mg/g to 300 mg/g, particularly preferably from 80 mg/g to 275
mg/g, and a weight average molar mass Mw of from 8 kg/mol to 30
kg/mol. Preferably, the mass fraction of moieties derived from monomers
A, B, C, and D in the hydroxy functional copolymer 1 is from 5% to 35%
for A, from 15% to 40% for B, from 2% to 20% for C, and from 25% to 55%
for D, particularly preferred, from 10% to 25% for A, from 20% to 35% for
B, from 5% to 15% for C, and from 30% to 50% for D. If there are moieties
derived from monomer F, the mass fraction for F is from 0.1% to 1%,
particularly preferred, from 0.2% to 0.8%. If there are moieties derived
from monomer G, the mass fraction for G is from 2% to 20%, particularly
preferred, from 5% to 15%.

[0025]The acid functional copolymer 2 preferably has an acid number of
from 100 mg/g to 300 mg/g, particularly preferably from 120 mg/g to 260
mg/g, and a weight average molar mass Mw of from 8 kg/mol to 25
kg/mol. Preferably, the mass fraction of moieties derived from monomers
A, D, and E in the acid functional copolymer 2 is from 25% to 80% for A,
from 10% to 40% for D, and from 10% to 50% for E, particularly preferred,
from 30% to 65% for A, from 15% to 35% for D, and from 15% to 40% for E.

[0026]The mixture of the esterification product 12 of the hydroxy
functional copolymer 1 and the acid-functional copolymer 2 with the
unreacted amounts of these copolymers 1 and 2 preferably has a hydroxyl
number of from 40 mg/g to 250 mg/g, particularly preferably from 60 mg/g
to 200 mg/g, an acid number of from 15 mg/g to 80 mg/g, particularly
preferably from 20 mg/g to 70 mg/g, and a weight average molar mass
Mw of from 9 kg/mol to 40 kg/mol.

[0027]Neutralisation can be effected with aqueous alkali, and preferably,
with ammonia, and organic amines, especially tertiary amines, such as
N-methyldiethanolamine, N,N-dimethylethanolamine, and triethanolamine.

[0028]The binders obtained are preferably formulated to clearcoat paints
or pigmented paints. Usual additives such as defoamers, levelling agents,
wetting agents, and coalescing agents, crosslinkers such as those based
on aminoplast compounds and isocyanates, and in the case of pigmented
paints also dispersing agents and antisettling agents, can be used.

[0029]Paints formulated with the binders of the invention are particularly
useful for outdoor applications because of their low propensity to
yellowing, and their light stability.

EXAMPLES

Example 1

[0030]Hydroxy functional (meth)acrylic copolymers 1 have been prepared
from monomer mixtures as stated in Table 1. For the comparative (C1 and
C2) examples, the monomers indicated (second group in the table) together
with the initiator solution (third group in the table) were added to the
solvent as indicated (first group in the table), during five hours at
95° C., and reacted after the end of the addition for a further
two hours. After cooling, the reaction mass was diluted with further
butanol to a mass fraction of solids of about 65%.

[0031]For the inventive (1a, 1b and 1c) examples, the monomers indicated
(second group in the table) together with the initiator solution (third
group in the table) were added to the mixture of ε-caprolactone
and solvent as indicated (first group in the table), during five hours at
155° C., and reacted after the end of the addition for a further
four hours. After cooling to 80° C., the reaction mass was diluted
with further butanol to a mass fraction of solids of about 65%.

[0032]Carboxyl functional acrylic polymers 2 have been prepared from
monomer mixtures as stated in Table 1. The monomers indicated (second
group in the table) together with the initiator solution (third group in
the table) were added to the solvent as indicated (first group in the
table), during six hours at 95° C. (azobis isobutyronitrile, AIBN,
as initiator) or 115° C. (t-butyl peroctoate as initiator), and
reacted after the end of the addition for a further two hours. After
cooling, the reaction mass was diluted with further alcohol to a mass
fraction of solids of about 50%.

[0033]The polymer solutions of Examples 1 and 2 were mixed in the ratios
stated in Table 3, heated to about 120° C. whereupon the solvent
was distilled off under slightly reduced pressure until a mass fraction
of solids of at least 95% was reached. The mixture was held at this
temperature of between 100° C. and 120° C. until the
polymer was water-reducible (no formation of sediment during two hours of
observation time) after full neutralisation with dimethyl ethanolamine,
and a dispersion of an average particle size of less than 150 nm was
obtained, as determined with dynamic light scattering in a "particle
sizer". After the end of the reaction, the product was cooled,
neutralised with the said amine, and slowly diluted with deionised water
under formation of an aqueous dispersion.

[0034]White pigmented coating compositions 4a through 4d have been
prepared according to the recipe stated in the top section of Table 4.
Binders 3a through 3d of Example 3 were mixed and milled with the white
pigment (titanium dioxide, ®Kronos 2310, Kronos Titan GmbH), a
wetting agent having both nonionic and ionic hydrophilicity (®Additol
VXW 6374, Cytec Surface Specialties Austria GmbH), a defoamer
(®Surfynol 104 E, nonionic wetting agent based on acetylene diol, Air
Products) and a silicone based levelling agent (®Additol VXL 4930,
Cytec Surface Specialties Austria GmbH). Butyl diglycol was added as
coalescing adjuvant, and deionised water was used to reduce to a mass
fraction of solids of about 58%.

[0035]According to the recipe stated in the middle section, for the
preparation of the paint, further quantities of the same binders were
added to the pigment pastes thus prepared, together with an imino, mixed
ether type melamine resin, ®Maprenal VMF 3924 (Ineos Melamines GmbH),
and other additives as stated in the table.

[0036]After addition of the crosslinker and other additives, further
deionised water was added in an amount such that the efflux time from a 4
mm cup (according to DIN 53 211) was adjusted to thirty seconds for all
paints.

[0037]The following properties were found:upon application of a 200 μm
wet film onto a glass plate, drying for ten minutes at room temperature,
ten minutes of forced drying at 80° C., and further twenty-five
minutes of forced drying at 130° C., as shown in Table 5a

[0038]While the addition of long chain alkyl methacrylate to the binder
polymer (paint 4) increases the gloss and reduces the haze of the coating
prepared with the said binder, the pendulum hardness is impaired by such
addition. Combination (paint 3) of long chain alkyl methacrylate and
caprolactone retains the hardness level of the unmodified binder (paint
1) while having the favourable gloss and haze properties of the long
chain alkyl methacrylate modified binder. Addition of caprolactone alone
(paint 2) increases the gloss while leaving the hardness unchanged, but
there is a significant increase in haze.

[0039]In a further paint test, the paints were poured onto a glass plate,
to yield a coating with a dry film thickness of 30 μm, dried for ten
minutes at room temperature, ten more minutes of forced drying at
80° C., and further twenty-five minutes of forced drying at
130° C., coatings with properties as shown in Table 5b were
obtained.

[0040]For hardness, gloss, and haze, virtually the same results as in 5a
have been obtained. Wave Scan is a method to judge the surface quality,
especially freedom from defects and "orange peel" structure. Low values
in this test for both short and long wave mean that the surface appears
faultless.

[0041]The mechanical properties were tested on a coating on a steel sheet,
with a 40 μm dry film thickness. The paint was applied by spraying,
and subsequently dried (ten minutes at room temperature, ten minutes at
80° C., and further twenty-five minutes at 130° C. The
values found are listed in table 5c.

[0042]While paint 2 already shows better gloss when compared to a paint
where the binder does not comprise the epsilon caprolactone (comparative
paint 1), further improvement can be seen in paints 3 and 4 where not
only the gloss is higher than that of the comparative paint 1, there is
also a marked reduction in haze. The highest gloss and lowest haze are
found in paints (3) that comprise both the epsilon caprolactone and the
long chain alkyl methacrylate. See Table 5c.

[0043]Likewise, while the hardness is on par with that of the comparative
coating (paint 1), also the wave scan is reduced, in one aspect each for
paints 2 and 4, and both in long and short wave, in paint 3. This
synergistic behaviour could not have been expected.

[0044]Also, the mechanical properties and adhesion are favourably
influenced, with a synergistic effect for paint 3 also shown in Erichsen
cupping and Cross Cut Test (DIN EN ISO 2409).

Patent applications by Johann Billiani, Graz AT

Patent applications by Rami-Raimund Awad, Graz AT

Patent applications by Cytec Surface Specialties Austria Gmbh

Patent applications in class Acid or ester contains an oxygen atom which is other than part of a free carboxyl group or carboxylic acid ester group

Patent applications in all subclasses Acid or ester contains an oxygen atom which is other than part of a free carboxyl group or carboxylic acid ester group